1. Field of the Invention
Embodiments of the present invention generally relate to handling tubulars and drilling into a formation to form a wellbore. More particularly, embodiments of the present invention relate to drilling with casing. Even more particularly, embodiments of the present invention relate to drilling with casing and cementing the casing into the formation.
2. Description of the Related Art
In conventional well completion operations, a wellbore is formed to access hydrocarbon-bearing formations by the use of drilling. In drilling operations, a drilling rig is supported by the subterranean formation and used to urge a drill string toward the formation. A rig floor of the drilling rig is the surface from which drilling strings with cutting structures, casing strings, and other supplies are lowered to form a subterranean wellbore lined with casing. A hole is formed in a portion of the rig floor above the desired location of the wellbore. The axis that runs through the center of the hole formed in the rig floor is the well center.
Drilling is accomplished by utilizing a drill bit that is mounted on the end of a drill support member, commonly known as a drill string. To drill within the wellbore to a predetermined depth, the drill string is often rotated by a top drive or rotary table on the drilling rig. After drilling to a predetermined depth, the drill string and drill bit are removed and a section of casing is lowered into the wellbore.
Often, it is necessary to conduct a pipe handling operation to connect sections of casing to form a casing string which extends to the drilled depth. Pipe handling operations require the connection of casing sections to one another to line the wellbore with casing. To threadedly connect the casing strings, each casing section must be retrieved from its original location, typically on a rack beside the drilling platform, and suspended above well center so that each casing section is in line with the casing section previously disposed within the wellbore. The threaded connection is made up by a device that imparts torque to one casing section relative to the other, such as a power tong or a top drive. The casing string formed of the two or more casing sections is then lowered into the previously drilled wellbore.
It is common to employ more than one string of casing or section of casing in a wellbore. In this respect, the well is drilled to a first designated depth with a drill bit on a drill string. The drill string is removed. Sections of casing are connected to one another and lowered into the wellbore using the pipe handling operation described above to form a first string of casing longitudinally fixed in the drilled out portion of the wellbore. The first string of casing may then be cemented into place within the wellbore by a cementing operation. Next, the well is drilled to a second designated depth through the first casing string, and a second, smaller diameter casing string or string of casing comprising casing sections is hung off of the first string of casing or section of casing. A second cementing operation may be performed to set the second string of casing within the wellbore. This process is typically repeated with additional casing sections or casing strings until the well has been drilled to total depth. In this manner, wellbores are typically formed with two or more strings of casing.
It is known in the industry to use top drive systems to rotate the drill string to form the wellbore. The quill of the top drive is typically threadedly connected to an upper end of the drill pipe in order to transmit torque to the drill pipe.
As an alternative to the conventional method, drilling with casing is a method often used to place casing strings within the wellbore. This method involves attaching a cutting structure typically in the form of a drill bit to the lower end of the same string of casing which will line the wellbore. Drilling with casing is often the preferred method of well completion because only one run-in of the working string into the wellbore is necessary to form and line the wellbore for each casing string.
Drilling with casing is typically accomplished using a top drive powered by a motor because the top drive is capable of performing both functions of imparting torque to the casing string to make up the connection between casing strings during pipe handling operations and of drilling the casing string into the formation. A problem encountered with top drive systems is the potential for damage to the threads of the drill pipe or casing. Damage to the casing threads is problematic because the casing connections must remain fluid and pressure tight once the drilling operation has been completed.
Gripping heads have been developed for gripping casing to prevent damage to the threads. The top drive is connected to a gripping head, which may be an external gripping device such as a torque head or an internal gripping device such as a spear. A torque head is a type of gripping head which grips the casing by expanding a plurality of jaws or slips against an exterior surface of the casing. A spear is a gripping head which includes slips for gripping an interior surface of the casing.
Gripping heads generally have a top drive adapter for connection to a top drive quill. In this respect, torque may be transmitted to the casing with minimal damage to the threads of the quill.
The gripping head has a bore therethrough through which fluid may flow. The gripping head grippingly engages the casing string to serve as a load path to transmit the full torque applied from the top drive to the casing string.
The top drive and the gripping head, when the gripping head grippingly engages the casing, function as the means for rotating the casing string, means for providing a sealed fluid path through the casing string, and means for lowering the casing string into the wellbore. To function as the means for lowering the casing string into the wellbore, the top drive is disposed on rails so that it is moveable axially in the plane substantially in line with well center. The rails also help the top drive impart torque to the casing string by keeping the top drive rotationally fixed.
Because the casing string is rotated by the top drive, the top drive also carries the tensile load of the casing string. Therefore, the top drive connection may be a limiting factor in the load that is actually applied. For example, the connection between the top drive and the torque head may limit the tensile load supportable by the top drive. The problem is exacerbated when drilling with casing because a casing typically weighs more than a drill pipe. As a well is drilled deeper, the tensile load of a drilling string of casing will increase faster than a drill string of drill pipe. Therefore, the drilling with casing operation may be prematurely stopped because the weight and drag of the casing drill string exceeded the tensile load rating of the top drive connection.
One proposed method of overcoming this problem is to increase the size of the threaded connection. While many drilling apparatus may be redesigned with a larger size threaded connection to increase its tensile load capacity, it is very costly and inefficient to redesign or replace a top drive already existing on a rig.
There is a need, therefore, for an apparatus for increasing the drilling capacity of a top drive. There is a further need for an apparatus that isolates the tensile load from the top drive connection. There is also a need for an apparatus for isolating tensile load that can be retrofitted with existing top drives.
During a typical drill pipe drilling operation, it is usually necessary to circulate drilling fluid while drilling the drill string into the formation to form a path within the formation through which the drill string may travel. Failure to circulate drilling fluid while drilling into the formation may cause the drill string to stick within the wellbore; therefore, it is necessary for a fluid circulation path to exist through the drill string being drilled into the formation.
When running a typical casing string into a drilled wellbore, fluid is often circulated to prevent the casing string from sticking. Thus, a circulating tool is used within the casing string to circulate fluid through the casing string while running the casing string into the drilled wellbore.
When it is desired to run the casing into the drilled out wellbore, the circulating tool is hooked up to the top drive and disposed within the casing string to allow circulation of the fluid. A check valve disposed in the bore of the circulating tool allows fluid flow from the surface of the well, through the casing string, and through the annular space between the outer diameter of the casing string and the formation, while preventing fluid from flowing back up through the check valve to the surface. The circulating tool further includes a packer or cup(s), usually an inflatable packer, disposed on its outer diameter. The packer is deployed to expand radially outward from the circulating tool to sealingly engage the inner diameter of the casing string. The packer and cup(s) seal the annular space between the outer diameter of the circulating tool and the inner diameter of the casing string; consequently, the packer isolates the inner diameter of the casing string below the packer to permit fluid under pressure to flow through the casing string and up through the annular space between the outer diameter of the casing string and the formation.
After the circulating tool is used to run the casing string to the desired depth within the formation, the casing string is often cemented into the wellbore at a certain depth before an additional casing string is hung off of the casing string so that the formation does not collapse onto the casing string due to lack of support. Furthermore, the casing string is often cemented into the formation once it reaches a certain depth to restrict fluid movement between formations. To cement the casing string within the wellbore, a cementing tool including a cementing head is inserted into the casing string to inject cement and other fluids downhole and to release cement plugs. The cementing head typically includes a plug releasing apparatus, which is incorporated into the cementing head above the wellbore. Plugs used during a cementing operation are held at the surface by the plug releasing apparatus. The typical cementing head also includes some mechanism which allows cement or other fluid to be diverted around the plugs until plug release is desired. Fluid is directed to bypass the plugs in some manner within the container until it is ready for release, at which time the fluid is directed to flow behind the plug and force it downhole.
The cementing head including an upper cement plug and a lower cement plug is used to cement the wellbore. The cement plugs typically define an elongated elastomeric body used to separate cement pumped into the wellbore from fluid ahead of and behind the cement. The lower cement plug has radial wipers to contact and wipe the inside of the casing string as the plug travels down the casing string. The lower cement plug has a cylindrical bore therethrough to allow passage of cement. The cylindrical bore is typically closed to flow with a rupture or breakable disc or diaphragm. The disc or diaphragm breaks or ruptures when the lower plug lands on a barrier to allow the passage of cement through the plug.
The lower cement plug is typically pumped ahead of the cement. After a sufficient volume of cement has been placed into the wellbore, an upper cement plug is deployed. Using drilling mud, cement, or other displacement fluid, the upper cement plug is launched or pumped into the bore of the casing string. The upper cement plug is then pumped down the casing with displacement fluid, typically mud or water. As the upper cement plug travels downhole, it displaces the cement already in the bore of the casing to the annular area defined as the external casing diameter and the borehole. When the upper plug arrives at the barrier, it seats against the lower cement plug already landed on the barrier, closing off the internal bore through the lower cement plug, thus stopping flow into the annular area.
To perform a cementing operation, the circulating tool must be retrieved from the casing string and set aside before the cementing tool can be installed on the casing string. The casing string is typically supported by a spider which grippingly engages the outer diameter of the casing string on the rig floor at well center. Then, an entirely separate cementing tool is installed on the casing string by being threadedly connected or clamped onto an upper portion of the casing string to perform a cementing operation.
When using a separate cementing tool, extra time is necessary to rig down the gripping head and circulation tool and then rig up the cementing tool when it is desired to cement the casing string into the formation. Extra time results in extra labor and money spent on the operation. Using a separate cementing tool to conduct a cementing operation also requires the hardware for the circulating tool as well as the additional hardware for an entirely separate cementing tool.
There is a need for an integrated apparatus which adapts the top drive for gripping casing and includes circulating and cementing functions. There is a need for a means for gripping and rotating casing as the casing string is constructed (e.g., making up or breaking out the threaded connection between casings), as well as a means for rotating the casing during the drilling operation. There is also a need to decrease the amount of time between the drilling into the formation and the cementing of the casing into the formation. There is a further need to decrease the amount of hardware necessary at the drilling rig to drill into the formation and cement the casing into the formation.